Bender type transducers



Feb. 24, 1970 H. J. STRAUBE 3,497,731

BENDER TYPE TRANSDUCERS Filed Sept. 19, 19s? \\K\\ 1 L9 PowER (EFFICIENCY) F/'g 2 HIGH "0" (DEVICE l0 WITHOUT RESISTOR 2o) (DEVICE l0 WITH RESISTOR 20) l (Kc) EFFICIENCY vs FREQUENCY HELMUTJ. smu

United States Patent Office 3,497,731 BENDER TYPE TRANSDUCERS Helmut J. Straube, Monroe County, N.Y., assignor to General Dynamics Corporation, a corporation of Delaware Filed Sept. 19, 1967, Ser. No. 668,964 Int. Cl. H01v 7/00 US. Cl. 310-8.2 7 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to electromechanical transducer apparatus and more particularly to bender type transducers used in sonar applications.

A typical transducer of the bender type may include a pair of bonded active components in the form of juxtaposed piezoelectric ceramic disks or plates mounted so as to undergo flexure when subjected to acoustic energy. This flexure gives rise to an electrical voltage between electrodes on opposite faces of each disk, which voltage is representative of the acoustic energy impinging upon the disks. The transducer may also be used as a sound projector for converting alternating electrical energy into compressional wave energy or acoustic energy. The ceramic disks generate acoustic energy by bending in response to an applied electrical signal voltage.

There are many transducer applications where low power wide band frequency operation is desirable. Often there is a requirement for such a low power transducer to be employed in conjunction with measurement instrumentation.

Normally, as the operating frequency is reduced, a high radiation resistance is needed to obtain a wide band frequency operation. This is normally accomplished by increasing the size of the radiating surface, thereby increasing the size of the devices in which the transducer is embodied. This is at cross purposes with the often imposed requirement that transducers be relatively small in size and weight.

Accordingly, it is an object of the present invention to provide an improved bender type transducer with relatively small physical dimensions and which has a wide band frequency operation.

It is a still further object of the present invention to provide an improved transducer for converting mechanical force into electrical outputs and vice versa (converting electrical input signals into a mechanical output).

Briefly described, in one embodiment of the present invention a bender transducer includes a frame for mounting a series of vibratile assemblies each of which in turn mounts an electrical responsive device such as a piezoelectric ceramic element. A piston radiator and a mechanical resistor assembly are also connected to the vibratile assemblies so that in operation, the mechanical resistance assembly causes a loss of mechanical energy which lowers the Q of the transducer thereby providing for broad band frequency operation.

The provision of mechanical resistor assemblies in accordance with the invention reduces the efficiency in a region near the resonant frequency but actually increases efficiency at operational frequencies which substantially depart from the resonant frequency. This is true especially where the transducer is operated in a low frequency range.

3,497,731 Patented Feb. 24, 1970 A feature of mechanical resistors in accordance with the invention is that they may produce substantially pure mechanical resistance Without adding significant compliances or mass to the vibratile elements of the transducers, which are not wanted.

Another important feature of an apparatus according to the invention is that it in off-resonance operation decreases distortion of the wave form of its output signals.

I The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof will become more readily apparent from a reading of the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a bender transducer in accordance with the present invention;

FIG. 2 is a cross-sectional view of still another embodiment of a bender transducer in accordance with the present invention; and

FIG. 3 is a graph showing efficiency versus frequency for the transducer shown in FIG. 1, assembly and a similar structure Without a mechanical resistor.

Referring first to FIG. 1, there is shown an electromechanical bender transducer 10 which comprises a waterproof type frame or housing 14 including a hollow cylindrical member 15, a ring shaped member 16 formed of some insulating material having a channel shaped cross section and which is mounted in a circular groove formed in the interior surface 18 of the member 15. The member 16 snugly receives the end portion of two vibratile assemblies 19 and a mechanical resistor assembly 20. This is accomplished by means of two spacer rings 23 which are force fit into position and thereby fixedly secure the end portions of the vibratile assemblies 19 and the mechanical resistor assembly 20 to the frame 15.

A flexible diaphragm or sealing ring 24 is mounted about the forward front end of a radiating piston 26 (which may be of conventional configuration) and provides a fluid seal for the interior hollow portion of the member 15. The radiating piston member 26 flares downwardly from its top exposed end into the interior of the member 15 and terminates in an extended cylindrical portion 26b which extends through centrally disposed holes, which are formed in the assemblies 19' and the mechanical resistor assembly 20, and terminates in a free end portion 260 which is threaded and receives a nut 28 which fixedly secures the radiating piston 26 to the mechanical resistor assembly 20. Separating washers 29 are provided between the two vibratile assemblies 19 and after the nut 28 is securely tightened, motion of the piston 26 will be transferred to the assemblies 19 and 20'. It will be clear to those skilled in the art that other means could be employed to connect the mechanical resistor assembly 20 to the vibratile assemblies of the transducer than the preferred illustrated arrangement.

Only one vibratile assembly 19 need be described inasmuch as both are identical in construction. The fleXural vibratile assembly 19 (washer-shaped) includes a driven vibrating portion 35, a stationary peripheral or rim portion 36 fixedly secured in the frame 15 and a hinge portion 37 defined by two similar (equal in depth) coaxial grooves 38 and 39 disposed in a back-to-back relationship on major faces 41 and 42 respectively of the vibratile assembly 19 and encircle the entire portion 35 separating it from the end portion 36. Also formed within the portion 35 are coaxial channels 43a and 4312 which are of equal depth and encircle the discoid driven portion 35, and are adapted to receive electrically responsive devices such as piezoelectric ceramic disks 44a and 44b. The flexural vibratile assembly 19 may (with the exception of the disks 44) be made of an elastic resilient material such as spring steel, Phosphor bronze, or the like.

The hinge portion 37 is relatively compliant to lateral movement of the major faces 41 and 42 or to fiexnre of the driven portion 35. The hinge portion 37 however is substantially rigid for end thrust or piston-like movement of the radiating portion 35. Moreover, the hinge portion 37 provides an edge support for the radiating portion 35. Accordingly, inasmuch as the vibratile assembly 19 is fixed at the rim portion 36, the driven portion 35 can be excited into flexural vibrations about the hinge portion 37. A complete discussion of the hinge portion 37 may be found in my co-pending U.S. patent application Ser. No. 407,685 for Electromechanical Apparatus filed Oct. 30, 1964, and owned by the assignee of the present invention, and a more complete detail of the features and advantages of the channels 38 and 39 may be found in my co-pending U.S. patent application Ser. No. 452,052 filed Apr. 30, 1965 and owned by the assignee of the present invention.

The mechanical resistive assembly comprises an elastic cylindrical disphragm 50 (which is washer-shaped) preferably formed from a lossy material such as neoprene, polyurethane or some other synthetic rubber material and which is press-fit into channels 51 and 52 respectively provided by outer and inner rings 54 and 56. Alternatively, the diaphragm 50 may be bonded to the outer and inner rings 54 and 56. The outer ring is fixedly mounted in the insulated member 16 of the frame 14, whereas the inner ring provides a bearing surface for the cylindrical portion of the radiating piston and also a bottom bearing surface for the nut 28. With the outer ring 54 clamped and the inner ring 56 moving, molecular friction within the diaphragm 50 causes a loss of mechanical energy of the transducer lowering the Q of the transducer as will be described more fully in connection with the discussion of FIG. 3. By choosing different materials forming the diaphragm 50 and varying its dimensions, the resistance provided by the mechanical resistive assembly 20 may be greatly changed. Moreover, it has been found that if the diaphragm is provided by a series of superposed layers of an elastic material (one on top of the other), that this laminar arrangement substantially increases the resistance of the mechanical resistive assembly 20 due to the high resistance to motion between the layers.

In .operation as the ceramic piezoelectric devices 44a and 44b expand and contract in response to electrical signals, the center part of the elastic diaphragm 50 will deflect more near the region of the cylindrical extension 26b of the piston 26 than adjacent the frame 14 thereby providing a substantial mechanical resistance to the movement of the piston radiator 26. It should be understood that the choice of materials and transmissions of the elastic diaphragm will substantially effect the magnitude of the mechanical resistance to motion thereby changing the Q of the system. FIG. 3 depicts this feature by actually showing the contrast between similar transducers one of which employs the mechanical resistor assembly 20 and the other of which does not. As shown the mechanical resistor 20 causes a reduction in the efficiency of the system but lowers the Q of the transducer thereby providing for more efficient operation at frequencies which the transducer may be used in a low power operation, which is by way of example only but without limitation.

Turning now to FIG. 2, a bender type transducer 10' is shown which is similar to that shown in FIG. 1 (where similarities exist primed numerals will be used) with the exception that only a single vibratile assembly 19 is provided which receives only a single electrically responsive piezoelectric element 26'. The transducer may include a face seal 62 which is formed of an elastic material and which performs a similar radiating role to the piston 26 (discussed above). The seal 62 is bonded to the vibratile assembly 19' and the frame 14. An elastic diaphragm 50 is bonded to the bottom surface of the radiating portion 35' of the vibratile assembly 19 when the portion 35' flexes about the hinge 37, the molecular motion within the diaphragm 50' resists motion. The resistance of this elastic diaphragm 50 may also be controlled by varying the choice of its material and its dimensions.

While various embodiments of the invention have been described, variations thereof and modifications therein within the spirt of the invention will undoubtedly suggest themselves to those skilled in the art. For example, although the embodiment shown in FIG. 1 includes but a single mechanical resistor assembly 20, it will be understood that a transducer with a plurality of such assemblies 20 could also be provided in accordance with the invention. Accordingly, the foregoing description should be taken as illustrative and not in any limiting sense.

What is claimed is:

1. An electromechanical transducer of the bender type comprising (a) a frame,

(b) a flexural vibratile assembly including a rim portion secured to said frame and a driven radiating portion interconnected to said rim portion,

(0) an electrically responsive device secured to said vibratile member, and

(d) mechanical resistor means interconnected with said vibratile member and adapted to lower the mechanical Q of the transducer by dissipating power.

2. The invention as set forth in claim 1 wherein said mechanical resistor means comprises an elastic member which is mounted on said vibratile assembly.

3. The invention as set forth in claim 1 wherein said rim portion of said vibratile assembly is fixedly secured Within said frame and said vibratile assembly includes a hinge portion interconnecting said stationary rim portion to said driven radiating portion whereby fiexure occurs about said hinge portion.

4. The invention a set forth in claim 3 wherein said transducer includes a radiating piston having an elongated portion secured to the driven radiating portion of said vibratile member and said mechanical resistor means.

5. The invention as set forth in claim 4 wherein said resistor means comprises an outer ring fixedly mounted in said frame and an inner ring secured to said elongated portion and a disk shaped element of elastic material secured between said outer and inner rings.

6. The invention as set forth in claim 5 wherein said mechanical resistor means includes a plurality of said disk shaped members mounted together to provide a laminar structure.

7. The invention as set forth in claim 6 wherein said transducer includes a plurality of flexural vibratile assemblies, each of which has a cavity for receiving a said electrically responsive device.

References Cited UNITED STATES PATENTS 2,928,068 7/1960" Samsel 340--10 3,002,179 9/1961 Kuester 3l09.l 3,230,503 1/1-966 Elliot 340-40 3,255,431 6/1966 Howatt 3 l09.l 3,281,769 10/1966 Hueter 340l0 3,281,770 10/1966 Sims 340l0 3,382,841 5/1968 Bouyoucos 340-10 3,284,761 11/1966 Douglas 31010 3,337,843 8/1967 Kendig 340-l0 3,353,150 11/1967 Jocox 34010 3,427,481 2/1969 Lenahan 310-82 J D MILLER, Primary Examiner U.S. Cl. X.R. 

